The present invention relates to a system for monitoring the operation of a machine as it cycles through its operating sequence, and in particular to a system which diagnoses fault conditions and presents the nature and location of the fault condition to the machine operator in an easily discernible manner. In a particular embodiment of the invention, the system is employed with a plastics injection molding machine, although the invention has broader application to other types of machinery.
Present-day injection molding machines operate on a continuous basis to sequentially mold the plastic parts with little or no intervention on the part of the machine operator. The clamping mechanism first closes the two halves of the mold and the rotating plasticizing screw in the extruder plasticizes the plastic material until it is molten and at the same time retracts thereby building up a charge of molten plastic material in front of it. When the screw has retracted sufficiently to build up the proper charge of material and final clamping pressure has been exerted on the mold halves, the rotation of the screw is stopped and it is rammed forwardly by the injection cylinder to inject a charge of molten material into the mold. After the injected mass hardens sufficiently, the mold halves are opened by the clamping mechanism, and the finished part is ejected. This sequence of operations is then repeated each time that an additional part is molded.
Present-day injection molding machines, and other types of machinery such as die casting machines, are designed to cycle automatically under the control of an electronic controller. The controller has as inputs electrical signals from a large number of sensing devices, such as limit switches, pressure switches and relays, which are actuated when certain moving parts reach predetermined positions, or when the hydraulic pressure within a hydraulic cylinder exceeds or falls below predetermined limits, or when a timer associated with a particular operation of the machine times out. For example, the determination of when the movable platen for the mold is opened sufficiently to permit part ejection is made by a limit switch that is contacted either directly by the movable platen or by an element rigidly connected thereto. The attainment of final clamping pressure of the clamping mechanism sufficient to withstand the internal pressure within the mold during injection is sensed by a pressure actuated switch connected to the high pressure clamping cylinders. Generally, the output signals from these various sensing devices are connected by wires to the controller, which may be a very complex arrangement of relays, discrete electronic logic circuitry, or a programmable microprocessor. In a manner well known in the art, the controller reads the conditions on one or more of the inputs from the sensing devices, and if there are no fault conditions present, causes the machine to sequence through the next step, and when this has been accomplished, another group of inputs are monitored for the absence of fault conditions before the next step of the sequence is implemented.
When a fault condition is sensed by the controller, the operation of the machine is generally stopped immediately at that point, and the operator is advised of the presence of a fault condition by a visual and/or audible alarm. Unless a very sophisticated fault condition readout is employed, however, the operator will not be advised of the specific fault which has occurred, and the only indication that he will receive is that a fault condition is present. Most injection molding machines include an array of lights which are respectively associated with the various sensing and control solenoids, relays, timers and the like on the machine. When the respective solenoid or relay is activated, its associated light will be illuminated. Although the operator could check the light bank against a reference listing for the machine when a fault condition occurs to determine which relay, solenoid, timer, etc. has not activated when it should or has activated when it should not for that particular point in the machine sequence, this is a very complex procedure due to the large number of lights which will be illuminated at any one time.
When a malfunction occurs, the operator generally must rely on his experience and general knowledge of the operation of the machine to narrow down the possibilities for the fault condition. Once this is done and he determines at what point in the machine sequence the machine is presently in he can then check what he considers to be the possible causes for the malfunction by reading from the manual for the machine what output lights should be illuminated as against the actual condition of the lights on the light array. This is a trial and error technique, and greatly increases the machine down time necessary to correct the malfunction and resume normal operation of the machine. Although if the operator monitors closely the operation of the machine by observing directly the movement of the parts, he will be able to more rapidly localize the cause for the malfunction, experience has shown that most operators operating an automatic or semiautomatic machine do not pay close attention to each operating step of the machine. Monitoring the pattern of lights on the output array is even more difficult due to the large number of lights which are illuminated at any one time and the various combinations of lights, some of which will be illuminated more than once during the machine sequence.
With most prior art diagnostic systems of the type described above, a considerable amount of time is required for the operator to locate the malfunction before remedying the malfunction can even occur. Since the profitability of a molding operation depends, to a great extent, on the amount of poundage that can be processed over a period of time, the amount of time required to locate and cure a malfunction is critical. Furthermore, the plastic within the barrel during a cessation of operation of the machine is likely to become overheated and therefore unsuitable for use, and even damage to the machine may occur during the time that operation is halted.
Although very sophisticated microprocessors can continuously monitor and display the machine sequencing and provide for accurate location of the fault conditions, they are often quite expensive and difficult to implement in that special programming may be required. Some microprocessor controlled diagnostic systems include the ability to call up a specific portion of the machine's sequence on a CRT screen to aid in troubleshooting. For example, when a specific solenoid is not energizing, the operator selects the output associated with that solenoid, enters the output address through a keyboard, and the portion of the machine sequence associated with that output is displayed on the screen. The screen also indicates whether the contacts are open or closed in the specific sequence. Although the use of this type of a diagnostic system is much more rapid than physically checking between the machine manual and the output light array as discussed above, the operator must still take certain steps to localize the malfunction. A further disadvantage is that the operator may not be sufficiently skilled in the use of computer-type machinery to effectively utilize the microprocessor interface to locate fault conditions.
More sophisticated microprocessors have been used for monitoring the operation of machines, such as injection molding machines, wherein color bars or other display graphics can indicate the movement of the various machine parts as it cycles through its operation. The screen can also display faults which occur during the machine cycle. Although such microprocessor based systems convey a great deal of information to the operator, they are software implemented and relatively expensive.